Aristotle proposed a third option. In his Nicomachean Ethics, he described the idea of eudaemonic happiness, which said, essentially, that happiness was not merely a feeling, or a golden promise, but a practice. “It’s living in a way that fulfills our purpose,” Helen Morales, a classicist at the University of California, Santa Barbara, told me. “It’s flourishing. Aristotle was saying, ‘Stop hoping for happiness tomorrow. Happiness is being engaged in the process.’ ”

The finding is the latest in a series of related discoveries in the field of social genomics. In 2007, John Cacioppo, a professor of psychology and behavioral neuroscience at the University of Chicago, and Steve Cole, a professor of medicine at the University of California, Los Angeles, among others, identified a link between loneliness and how genes express themselves. In a small study, since repeated in larger trials, they compared blood samples from six people who felt socially isolated with samples from eight who didn’t. Among the lonely participants, the function of the genome had changed in such a way that the risk of inflammatory diseases increased and antiviral response diminished. It appeared that the brains of these subjects were wired to equate loneliness with danger, and to switch the body into a defensive state. In historical and evolutionary terms, Cacioppo suggested, this reaction could be a good thing, since it helps immune cells reach infections and encourages wounds to heal. But it is no way to live. Inflammation promotes the growth of cancer cells and the development of plaque in the arteries. It leads to the disabling of brain cells, which raises susceptibility to neurodegenerative disease. In effect, according to Cole, the stress reaction requires “mortgaging our long-term health in favor of our short-term survival.” Our bodies, he concluded, are “programmed to turn misery into death.”